1. Field of the Invention
The invention relates generally to the art of air-ride axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the ride and stabilize the vehicle during operation. More specifically, the invention relates to pneumatic control of the air springs of the air-ride axle/suspension systems, and in particular to a multi-stage height control valve for the air-ride axle/suspension systems which includes a position sensitive pilot signal that, for example, in one instance allows the height control valve to signal when a secondary ride height threshold has been reached to prevent further exhaustion of air from the air springs, and in another instance provides a pressure boost to relatively quickly re-inflate the air springs.
2. Description of Related Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers, typically include two or more leading or trailing arm suspension assemblies that connect the wheel bearing axles of the vehicle to the frame of the vehicle. Early suspension designs included heavy leaf-spring suspensions which resulted in a relatively rough ride to the cargo and/or passengers carried by the vehicle, and did not allow loads to equalize among the axles in all situations, thus creating the need for an axle/suspension system with softer ride characteristics and more efficient equalization characteristics. The subsequent development of air-ride axle/suspension systems provided greater load equalization among multiple axles for semi-trailers as well as improved ride quality for individual axles.
As a result, heavy-duty vehicles that transport freight often include leading or trailing arm air-ride axle/suspension systems, which use air springs to cushion the ride of the vehicle. Pneumatic control of these air springs is an important feature of air-ride axle/suspension systems. More particularly, it is important for a cushioned vehicle ride, and for optimum axle/suspension system performance and longevity to attempt to maintain a consistent predetermined distance between the vehicle frame and the travel surface. This predetermined distance is known in the art as the design ride height of the vehicle. The operating conditions of the vehicle must be considered in order to establish the design ride height of the vehicle. That is, when a heavy-duty vehicle executes certain maneuvers, such as making a hard turn or traveling over rough terrain, the forces imposed on the axle/suspension system by such maneuvers cause the axle/suspension system to articulate, or pivot and/or flex, beneath the vehicle frame which the system supports. Typically, an axle/suspension system is designed so that the anticipated range of articulation, pivoting and/or flexing occurs about a nominal predetermined position, and that nominal position is set as the design ride height of the vehicle. This articulation, pivoting and/or flexing can also be caused by the loading and unloading of the vehicle.
More specifically, after a heavy-duty vehicle is loaded with freight, or after freight is unloaded from the vehicle, the air springs of the axle/suspension system are adjusted to ensure that the vehicle is at design ride height. The adjustment of the air springs of the axle/suspension system is typically accomplished by a height control valve or leveling valve which is in fluid communication with an air source and with the air springs. When the vehicle is loaded with freight and the air springs of the axle/suspension system are compressed causing the vehicle frame to be positioned below design ride height or closer to the travel surface, compressed air is supplied to the air springs, thereby inflating/extending them and, in turn, causing the axle/suspension system to raise the vehicle frame to the design ride height. Conversely, when the vehicle is unloaded and the air springs of the axle/suspension system are extended, causing the vehicle frame to be positioned above design ride height or further away from the travel surface, air is exhausted from the air springs, thereby deflating/compressing them until the axle/suspension system lowers the vehicle frame to the design ride height. To control the flow of air into the air springs, and the exhaustion of air from the air springs, a mechanically operated valve typically is employed, and is known in the art as a height control valve or leveling valve. Adjustments to the height control valve and the linkage that controls activation of the valve enable the design ride height to be achieved before the vehicle travels over the road.
Also, as the vehicle travels over the road and the driver executes maneuvers that cause the axle/suspension system to articulate between positions that compress the air springs and positions that extend them, the height control valve acts to maintain the design ride height. That is, when the air springs are compressed, the height control valve supplies air to the air springs from a vehicle air reservoir. Conversely, when the air springs are in an extended position, the height control valve exhausts air from the springs to atmosphere. The amount of air that is supplied or exhausted is based on the duration of the articulation and the flow rate of the height control valve at a given position.
Subsequent prior art pneumatic control systems have typically included a solenoid valve which is incorporated into the pneumatic control system to allow the operator of the vehicle to dump or exhaust the air springs of the rear axle/suspension system in order to increase maneuverability of the vehicle in certain situations. Alternatively, the solenoid valve can also be incorporated in such a manner as to allow the air springs of the front and rear axle/suspension systems to be over-inflated in order to raise the height of the trailer, such as when the pneumatic control system is being used on a drop deck trailer or moving van having very low ground clearance. When configured to dump or exhaust the air springs of the rear axle/suspension system to increase maneuverability, the solenoid valve typically is in fluid communication with the conduit disposed between the height control valve and the rear air springs. In this particular configuration, the solenoid valve is utilized to exhaust the air springs of the suspension assemblies of the rear axle/suspension system when the vehicle operator encounters a situation that requires increased maneuverability of the heavy-duty vehicle, such as when the vehicle is being operated in an urban setting or when the vehicle is being maneuvered around a loading/unloading yard. More particularly, the solenoid valve is electrically connected to a control switch that is located in the cab of the heavy-duty vehicle. When the operator of the heavy-duty vehicle desires to exhaust the air springs of the rear axle/suspension system of the vehicle in order to increase maneuverability, the operator flips the control switch which sends an electrical signal or impulse to the solenoid valve. Once energized, the solenoid valve prohibits the flow of air from the height control valve to the air springs of the rear axle/suspension system and, instead, allows fluid or air in the air springs of the rear axle/suspension system to flow out through the solenoid valve to atmosphere. Typically, these prior art pneumatic control systems exhaust all of the air from the air springs of the rear axle/suspension system. By exhausting all of the air from the air springs of the rear axle/suspension system, the trailer longitudinal wheel base is effectively shortened, as the cargo loads which had previously been imparted approximately equally on both the front and rear axle/suspension systems are shifted forward toward the front axle/suspension system of the trailer.
Some problems associated with these prior art height control valves which are used in conjunction with pneumatic control systems that exhaust all of the air from the air springs of the rear axle/suspension system include difficulty on the part of the operator of the vehicle in determining when the rear axle/suspension system has become sufficiently exhausted so as to allow increased maneuverability of the vehicle. Another problem associated with such prior art valves and pneumatic control systems is relatively slow re-inflation of the air springs of the axle/suspension systems once the rear axle/suspension system dump control has been turned off. More particularly, when the operator of the vehicle desires to dump the air springs of the rear axle/suspension system to increase the maneuverability of the vehicle, the operator flips the cab switch and the solenoid valve is energized to allow air from the air springs of the rear axle/suspension system to exhaust to atmosphere. In this situation, all of the air in the air springs of the rear axle suspension system is exhausted. The prior art height control valve does not have the capability to limit or stop the exhaustion of air from the rear air springs once a sufficient lowered ride height has been reached. Moreover, when the operator of the vehicle flips the cab switch to de-energize the solenoid valve in order to once again route air from the air reservoir tank through the height control valve to the rear air springs, the pressure in the air springs of the front axle/suspension system must first drop as the pressure in the front and rear air springs reaches equilibrium. The amount of time required for the air springs of the front and rear axle/suspension systems to re-inflate can be quite lengthy because, once the solenoid valve is de-energized and the front and rear air springs reach equilibrium, the height control valve must re-inflate all of the air springs simultaneously. The result of this simultaneous re-inflation of multiple air springs is that the trailer rides on the jounce stops or bumpers or below design ride height with limited suspension travel until sufficient air pressure is built up in the air springs of the front and rear axle/suspension systems to once again allow the vehicle to achieve design ride height. As set forth above, this can take a relatively significant amount of time, the result being that the operator of the vehicle may drive for some time with the vehicle being non-air supported or below design ride height. Operating the vehicle under these conditions potentially reduces axle/suspension system performance and longevity and might also lead to undesirable wear and possible premature failure of the components of the front and rear axle/suspension systems.
For solenoid valves which are used in conjunction with pneumatic control systems for drop deck trailers or moving vans configured to over-inflate the front and rear air springs in order to raise the height of the trailer, the solenoid valve is typically in fluid communication with the conduit disposed between the height control valve and the front and rear air springs. In this configuration, the solenoid valve is utilized to over-inflate the air springs of the front and rear axle/suspension systems when the vehicle operator encounters a situation that requires higher ground clearance, such as when the vehicle encounters raised sections of the road surface at railroad tracks and/or off-road conditions. This configuration is also utilized to raise drop deck trailers equipped with a slider so that the tires mounted on the axle/suspension system(s), which in turn are mounted on the slider, are able to clear the cut-outs for the wheel wells on the trailer, so that the slider can be moved longitudinally beneath the trailer. More particularly, the solenoid valve is electrically connected to a control switch that is located in the cab of the heavy-duty vehicle. When the operator of the heavy-duty vehicle desires to over-inflate the air springs of the front and rear axle/suspension systems of the vehicle in order to increase vehicle ground clearance and raise the height of the trailer, the operator flips the control switch which sends an electrical signal or impulse to the solenoid valve. Once energized, the solenoid valve prohibits the flow of air from the height control valve to the air springs of the front and rear axle suspension systems and, instead, allows air from the vehicle air reservoir to flow directly to the air springs of the front and rear axle suspension systems, bypassing the height control valve. Typically, these prior art pneumatic control systems over-inflate the air springs of the front and rear axle/suspension systems until the shock absorbers physically stop the vehicle from being raised any further. By over-inflating the air springs of the front and rear axle/suspension systems, the trailer is raised allowing the vehicle to negotiate high sections of the road surface, such as railroad tracks and/or off road conditions, and/or also providing clearance between the tires mounted on a slider axle/suspension system and the wheel well cut-outs on the trailer so that the slider can be moved longitudinally beneath the trailer.
Some problems associated with these prior art height control valves which are used in conjunction with pneumatic control systems that over-inflate the air springs of the front and rear axle/suspension systems include potential damage to the shocks and shock mounts as they are not designed to react the full force exerted on them by the front and rear air springs during over-inflation. Moreover, the air springs themselves can also be potentially damaged during the over-inflation because the air springs are not designed to be at high inflation pressures when fully extended. A regulator could be utilized by the operator of the vehicle to control how much pressure is introduced into the air springs during over-inflation, but this operation is dependent upon the operator of the vehicle and can still lead to over-stressing the shocks, shock brackets and/or air springs.
Therefore, a need exists in the art for a height control valve for the air springs of an air-ride axle/suspension system of a heavy-duty vehicle, which overcomes the deficiencies of the prior art height control valves which are used in conjunction with pneumatic control systems and which is capable of signaling, via a pilot port, when a secondary ride height has been reached by the vehicle in order to stop additional exhaustion of air from the air springs of the rear axle/suspension system during a rear axle dump, or alternatively, to stop excessive over-inflation of the front and rear air springs during an over-inflation event, and which is also capable of providing a pressure boost to re-inflate the air springs of the air-ride axle/suspension system configured for rear axle dump in order to quickly raise the vehicle back to the design ride height.